A Mix Design Procedure for Alkali-Activated High-Calcium Fly Ash Concrete Cured at Ambient Temperature

Department of Civil Engineering, Faculty of Engineering and Architecture, Rajamangala University of Technology Isan, Nakhon Ratchasima 30000, $ailand Civil Engineering Program, School of Engineering, University of Phayao, Phayao 56000, $ailand Program of Civil Technology, Faculty of Industrial Technology, Lampang Rajabhat University, Lampang 52100, $ailand Sustainable Infrastructure Research and Development Center, Department of Civil Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, $ailand Academy of Science, $e Royal Society of $ailand, Dusit, Bangkok 10300, $ailand


Introduction
Recently, alkali-activated binders have been widely studied to be used as a substitute for Portland cement.
is is because they show great promise as an environmentally friendly binder, have high strength, are stable at high temperatures, and have high durability which are similar to those of Portland cement [1,2].From the past, alkaliactivated binders are certainly emerged as a novel construction material and have a huge potential to become a prominent construction product of good environmental sustainability [3].Alkali-activated binders are normally obtained from amorphous aluminosilicate materials such as fly ash, calcined kaolin, or metakaolin activated with high alkali solutions [4][5][6][7][8].
e sodium aluminosilicate hydrate (N-A-S-H) gel is the main reaction product for the low-calcium system, while calcium silicate hydrate (C-S-H) and calcium aluminosilicate hydrate (C-A-S-H) gels coexisted with sodium aluminosilicate hydrate (N-A-S-H) gel are the main reaction products for the high-calcium system [7,9].In ailand, high-calcium fly ash (FA) from the Mae Moh power plant in the north of ailand is a widely used starting material for making alkali-activated binders.High CaO content from this FA is very attractive for making alkali-activated binders because it can enhance the strength development when cured at ambient temperature [10][11][12][13][14][15]. is is why alkali-activated binders are needed to be used in practical works.
It is well known that alkali activator solution is one of the most important factors influencing the strength development of alkali-activated binders.From previous study on this area by Pimraksa et al. [16], they reported that sodium hydroxide and sodium silicate solutions were widely used as liquid activators because of availability and good mechanical properties.Panias et al. [17] claimed that sodium hydroxide solution is commonly used for the dissolution of Si 4+ and Al 3+ ions from FA to form aluminosilicate materials, whereas sodium silicate solution contains soluble silicate species and thus is used to promote the condensation process of alkali-activated binders [13].Many researchers [6,13,[18][19][20] reported that a combination of sodium silicate and sodium hydroxide solutions showed the best mechanical performance of alkali-activated binders.
To be useful in practice, a mix design methodology of alkali-activated binders has been studied.For example, Lloyd et al. [21] conducted a mix design methodology for alkaliactivated low-calcium fly ash concrete.Ananda Kumar and Sankara Narayanan.[22] studied a design procedure for different grades of alkali-activated concrete by using Indian standards.In this method, fly ash content and activator solution-to-fly ash ratio were selected based on the strength requirement and by keeping the fine aggregate percentage as constant.Ferdous et al. [23] proposed a mix design for fly ashbased alkali-activated binders concrete by considering the concrete density variability, specific gravity of the materials, air content, workability, and the strength requirement.Also, Lahoti et al. [24] studied the mix design factor and strength prediction of metakaolin-based geopolymer, but it was just a study on the basic properties of the geopolymer made from metakaolin which were not applicable for other raw materials such as fly ash and slag.
ere were few research studies conducted by Anuradha et al. [22] and Ferdous et al. [23] that used the trial-and-error approach for considering a mix design of alkali-activated binders.However, mix design and proportion of containing binders of alkali-activated concrete seem to be complex because more variables are being involved in it.
erefore, there is no standard mix design method available for designing alkali-activated binders concrete to date.According to the recent study, Pavithra et al. [25] studied a mix design procedure for alkali-activated low-calcium FA concrete.It is shown that its strength follows a similar trend to that of Portland cement concrete as per ACI standards.However, this work still used the temperature curing for enhancing the strength development.From the literature review, there is no research investigated on a mix design methodology for alkali-activated high-calcium FA concrete.erefore, in this research, we attempt to make a new mix design methodology for alkali-activated high-calcium FA concrete.Many parameters, namely, NaOH concentration, alkaline activator solution-to-binder ratio, and coarse aggregate size, have been investigated.Engineering properties, that is, setting time, compressive strength, flexural strength, modulus of elasticity, and Poisson's ratio, of the AAHFAC have been tested to understand behaviors for utilizing this material in the future.e step-by-step procedure of the mix design for alkali-activated highcalcium FA concrete will be explained in this paper.e outcome of this study would lay a foundation for the future use of alkali-activated high-calcium FA concrete for manufacturing this material in construction work.

Materials.
e precursor used in this study is fly ash (FA) from lignite coal combustion.e FA is the byproduct from the Mae Moh power plant in northern ailand with a specific gravity of 2.65, a mean particle size of 15.6 µm, and a Blaine fineness of 4400 cm 2 /g, respectively.

Proposed Method for Designing Alkali-Activated High-
Calcium Fly Ash Concrete.In this paper, we propose a novel mix design methodology for alkali-activated high-calcium y ash concrete (AAHFAC) in a rational approach.It should be noted that the method is easy to use because it is based on the ACI 211.4R-93 [30] with some modi cation.e parametric studies are composed of di erent NaOH concentrations, alkaline activator solution-(AAS-) to-binder ratios, and coarse aggregate sizes.e ow chart for the mix design procedure in this study is illustrated in Figure 1. e step-bystep procedure is summarized as follows: (1) Step 1: selection of the maximum size of the coarse aggregate is step is to select the maximum sizes of coarse aggregates for mixing the AAHFAC.ree di erent sizes of coarse aggregates have been investigated, namely, 4.5-9.5 mm or average 7 mm, 9.5-12.5 mm or average 10 mm, and 12.5-20.0mm or average 16 mm.Advances in Materials Science and Engineering Step 2: selection of the alkaline activator solution (AAS) content and air content AAS content and air content were based on the maximum coarse aggregate size as per ACI standards.Maximum AAS and percentage of air per cubic meter of concrete in this study were selected by using the slump condition of around 20 mm as per ACI standards.is condition is summarized in Table 3.
(3) Step 3: adjustment of the alkaline activator solution (AAS) content due to percentage of void in the fine aggregate As per ACI 211.4R-93 [30], a mixture of concrete has been recommended to use the fine aggregate with fineness modulus values from 2.4 to 3.2.However, particle shape and surface texture of the fine aggregate have an effect on its voids content; therefore, mixing water requirements may be different from the values given.As mentioned, the values for the required mixing water given are applicable when the fine aggregate is used that has a void content of 35%.If not, an adjustment of water content must be added into the required water content.erefore, this study will calculate the AAS content due to percentage of void in the fine aggregate in a similar way to Portland cement concrete.is adjustment can be calculated using the following equation: where AAS adjustment is an adjustment of the AAS content (kg/m 3 ), ρ RS is the density of the fine aggregate in SSD condition (kg/m 3 ), S G is the specific gravity of the fine aggregate, and ρ w is the density of water (kg/m 3 ).
(4) Step 4: selection of alkaline activator solution-to-fly ash (AAS/FA) ratio is research attempts in adopting the standard AAS-to-FA ratio curve of the AAHFAC before use.e minimum compressive strength could be determined from the relationship between 28-day compressive strength and AAS-to-FA ratio.Only the compressive strength of AAHFAC was considered as it is the requirement as per ACI 211.4R-93 [30].(5) Step 5: calculation of binder content e weight of the binder required per cubic meter of the AAHFAC could be determined by dividing the values of mixing the AAS content after an adjustment of the AAS content due to percentage of void in the fine aggregate.From the literature, NaOH and Na 2 SiO 3 were found to be the commonly used alkali activators [21].In this study, NaOH and Na 2 SiO 3 have been selected as alkaline activator solutions.According to Table 4, the density of NaOH with different concentrations has been used for calculating the volume of AAS as per the volume method.e individual mass of alkaline activator solutions content could be calculated using the following equation: (2) Step 7: calculation of fine and coarse aggregates e mass of fine and coarse aggregates content is determined as per the absolute volume method.Let the percentage of the fine aggregate in the total aggregate be 30% and that of the coarse aggregate be 70%.Fine and coarse aggregates content are determined using the following equation: where M RS is the mass of the fine aggregate (kg), M LS is the mass of the coarse aggregate (kg), S G(RS) is the specific gravity of the fine aggregate, S G(LS) is the specific gravity of the coarse aggregate, V FA is the volume of high-calcium fly ash, V NaOH is the volume of NaOH, V Na 2 SiO 3 is the volume of Na 2 SiO 3 , and V air is the volume of entrapped air.(8) Step 8: calculation of superplasticizer dosage e AAS has the higher viscosity than tap water when used for making the AAHFAC.Hardjito et al. [32] reported that the dosage of the superplasticizer was effective for the range between 0.8 and 2% of binder content to improve the workability of alkali-activated binder concrete.Pavithra et al. [25] also claimed that the use of superplasticizer dosage was found to have impact on behavior of fresh alkali-activated binder concrete; however, it had a little effect on strength and other properties.erefore, to improve the workability of the AAHFAC, a small amount of the superplasticizer was incorporated in the mixture.(9) Step 9: validation of strength attained with the proposed mix design e 28-day compressive strength obtained from testing will be verified with the target strength.(10) Step 10: recalculation of Step 4 by the strength obtained from Step 9 After the 28-day compressive strength has been obtained from testing, all strengths will be recalculated in Step 4 for determining the strength requirement of the AAHFAC with various AAS-to-FA ratios.(11) Step 11: validation of strength achieved Compressive strength tests will be conducted in the laboratory using the mix design proposed above.When the designed mix satisfies the strength requirement, the final development of the AAHFAC can be made by employing the above design steps.

Manufacturing and Testing of the AAHFAC.
e laboratory experiments have been conducted to validate the proposed mix design.Based on the AAHFAC trial mix, highcalcium fly ash (FA) from the Mae Moh power plant in northern ailand is used as a starting material for making the AAHFAC.Constant NaOH/Na 2 SiO 3 ratio is fixed at 1.0 in all mixes.
e AAHFAC has been manufactured with different NaOH concentrations of 10 M and 15 M.Both fine and coarse aggregates in saturated surface dry (SSD) condition have been used for making the AAHFAC.Crushed lime stone with different average sizes of 7, 10, and 16 mm, respectively, is investigated.In this present work, mix design of the AAHFAC with slump at around 17.5-22.5mm or average 20 mm has been controlled in order to ensure the workability of the AAHFAC.
For the mixing of the AAHFAC, fine and coarse aggregates were mixed together first for 60 s.After that, NaOH solution was added, and then, they were mixed again for 30 s.After 30 s, FA was added, and then, the mixture was mixed for 60 s.Afterward, Na 2 SiO 3 solution and superplasticizer were added into the mixture, and the mixture was mixed again for a further 60 s until becoming homogeneous.e mix proportions of the AAHFAC are illustrated in Table 5.
After mixing, the workability of the AAHFAC was tested using the slump cone test as per ASTM C143 [33] as shown in Figure 2. Setting time of the AAHFAC was evaluated using the method of penetration resistance as per ASTM C403/C403M-16 [34].After that, a fresh AAHFAC was placed into a cylinder mold with 100 mm diameter and 200 mm height to measure the compressive strength, modulus of elasticity, and Poisson's ratio.Tests for the determination of the static chord modulus of elasticity and Poisson's ratio of the samples have been carried out as per ASTM C469 [35].e 75 × 75 × 300 mm3 long beam was used to measure the flexural strength of the AAHFAC, and the flexural strength was calculated as per ASTM C78 [36].
e test setup for the compressive strength, flexural strength, modulus of elasticity, and Poisson's ratio of the AAHFAC is illustrated in Figures 3 and 4.After curing, the AAHFAC samples were demolded with the aid of slight tapping at the side of the mold at the age of 1 day and immediately wrapped with vinyl sheet to protect moisture loss and kept at the ambient room temperature.All samples of the compressive strength, flexural strength, modulus of elasticity, and Poisson's ratio were tested at the age of 28 days of curing of the AAHFAC.Five identical samples were tested for each mix, and the average value was used as the test result.Advances in Materials Science and Engineering

Experimental Results and Discussion
Figures 5-10 show the test results of fresh AAHFAC and mechanical properties of the AAHFAC.According to Figure 5, the slump values are between 18 and 22 mm; therefore, mix design of the AAHFAC from Table 5 is in line with the slump value at around 17.5-22.5mm.As mentioned, the AAS and air contents based on the maximum size of the aggregate as per the ACI standard could be taken for this study.e final setting time of the AAHFAC tends to obviously increase with the increase of AAS/FA ratio and NaOH concentration as illustrated in Figure 6. is result conforms to the previous studies [37,38] that an increase of fluid medium content resulted in less particle interaction and increased the workability of the mixture.Hanjitsuwan et al. [39] and Rattanasak and Chindaprasirt [40] also explained that NaOH concentration is a main reason for leaching out of Si 4+ and Al 3+ ions; therefore, the time of setting tends to increase.However, different sizes of the coarse aggregate are marginal changed in the setting time of the AAHFAC.Test results of the compressive strength, modulus of elasticity, and Poisson's ratio have been shown in Figures 7  and 8.It is found that the compressive and flexural strengths tend to increase with the increase of AAS/FA ratio and NaOH concentration; however, they are decreased with increasing coarse aggregate sizes.Sinsiri et al. [38] claimed that the excess OH − concentration in the mixture at high AAS/FA ratio causes the decrease of strength development of the AAHFAC similar to that in case of increasing water-to-cement ratios for Portland cement concrete.Also, the excess liquid solution could disrupt the polymerization process [37].For the effect of NaOH concentration, it is found that the increase in the leaching out of Si 4+ and Al 3+ ions from FA particles at high NaOH concentration could improve the N-A-S-H gel, and thus, it gives high strength development of the AAHFAC [40].Also, CaO oxide could react with silica and alumina from FA to form C-(A)-S-H gel which coexisted with N-A-S-H gel [11,12,14,15,20], resulting in an enhancement of strength.
e short setting time of less than 60 minutes at ambient temperature with relatively high 28-day compressive strengths of 16.0-36.0MPa indicated the role of calcium in the system.erefore, the AAHFAC could be used as an alternative repair material as reported by several publications [13,14,20,29,[41][42][43]. ere are many reasons such as high compressive strength [44], negligible drying shrinkage [45], low creep [46], good bond with reinforcing steel [47,48], good resistance to acid and sulfate [3,27], fire resistance [49], and excellent bond with old concrete [14,20,28].For the effect of coarse aggregate size, the strength development tends to decrease with the increase of coarse aggregate size.Generally,   6 Advances in Materials Science and Engineering the binder within the AAHFAC is an important factor on the strength development of the matrix.is agrees with the findings of Pavithra et al. [25] that the increase in total aggregate corresponding to the decrease of paste has an adverse effect on the strength development of low-calcium fly ash geopolymer concrete.
e experimental results obtained for the modulus of elasticity and Poisson's ratio of the AAHFAC mixes show an overall increase with the increase of compressive strength as shown in Figures 9 and 10; however, the coarse aggregate size influenced the modulus of elasticity and Poisson's ratio.Normally, it is well known that the values of modulus of elasticity and Poisson's ratio of concrete depend on the stiffness of paste and aggregates [50].
e modulus of elasticity obtained from this study agrees with Nath and Sarker [51] that the modulus of elasticity of geopolymer concrete with 28-day compressive strength of 25-45 MPa was between 17.4 and 24.6 GPa, while the modulus of elasticity of Portland cement concrete was between 25 and 35 GPa [51,52].According to Figure 10 Advances in Materials Science and Engineering all of the AAHFAC mixes is between 0.21 and 0.31.ey show values slightly higher than the values assigned for normal strength of Portland cement concrete which are between 0.11 and 0.21 [50].e high Poisson's ratios were associated with the mixes with large aggregates of 16 mm.For the mixes with smaller aggregates of 7 and 11 mm, Poisson's ratios are between 0.21 and 0.27 similar to the previously reported values of inorganic polymer concrete between 0.23 and 0.26 and also in the same range as those of high strength concrete between 0.20 and 0.25 [50].

Verification of the Mix Design Methodology Using Laboratory Experiments
To develop the mix design methodology of the AAHFAC, some parameters from laboratory experiments should be updated before use.In order to support the basic principles of mix design, the relationship between 28-day compressive strength and AAS/FA ratio from laboratory experiments has been produced as shown in Figure 11.e AAS/FA ratio curve can be determined for the minimum 28-day ese obtained strength requirements of the AAHFAC will be used to recalculate in Step 4 for determining the strength requirement of the AAHFAC with various AAS/FA ratios (Figure 11).
In order to verify the mix design procedure, an example design of the AAHFAC mix with the target 28-day compressive strength of 30 MPa has been considered.e parameters are NaOH concentration of 10 M, maximum aggregate size of 10 mm, and Na 2 SiO 3 /NaOH ratio of 1.0.Material properties of the AAHFAC ingredients are  Advances in Materials Science and Engineering illustrated in Table 2. e step-by-step procedure of the mix design is explained as follows: Step 1: selection of the maximum coarse aggregate size is mix design of the AAHFAC has been selected the maximum coarse aggregate size of 10 mm for mixing the AAHFAC.
Step 2: selection of AAS and air contents AAS and air contents are based on the maximum size of the coarse aggregate; therefore, AAS content of 225 kg/m 3 and air content of 3.0% have been used as given in Table 3.
Step 3: adjustment of AAS content due to percentage of void in the fine aggregate e fine aggregate used in this example has a void of 37%; therefore, the value of adjustment could be calculated as follows: erefore, the AAS content after an adjustment of AAS content due to percentage of void in the fine aggregate is 235 kg/m 3 .
Step 4: selection of AAS/FA ratio From Figure 11, for the minimum 28-day compressive strength of 30 MPa, it is found that the AAS/FA ratio of 0.50 is obtained when 10 M•NaOH was used as alkaline activator solution. Step Step 8: calculation of superplasticizer dosage Step 10: validation of strength achieved After following the mix design of the AAHFAC mix, the AAHFAC samples were tested for compressive strength on cylinder molds with 100 mm diameter and 200 mm height.After testing, it is found that the 28-day compressive strength of the AAHFAC is 31.15MPa.erefore, the mix design of the AAHFAC above meets the strength requirement.

Conclusion
In this study, the novel mix design methodology for alkaliactivated high-calcium fly ash concrete (AAHFAC) cured at ambient temperature in a rational way was proposed.From  Advances in Materials Science and Engineering the review of mix design of alkali-activated binders concrete, there is no standard mix design method available for designing the AAHFAC.Some works have been investigated in this area in an attempt to develop mix design methodology for alkali-activated low-calcium fly ash.However, it still used the temperature curing for enhancing the strength development of alkali-activated low-calcium fly ash, but this is limited for construction work.To be useful in practice, alkali-activated binders concrete cured at ambient temperature has been used to solve this problem.In this study, a new mix design methodology for AAHFAC was modified from ACI standards.e step-by-step procedure of the mix design for the AAHFAC mixes has been explained in the earlier section.From laboratory experiments, the 28-day compressive strength of the AAHFAC cured at ambient temperature ranging from 15 to 35 MPa was obtained.After compressive strength was obtained, the alkaline activator solution-to-binder ratios were used to modify the mix design of the AAHFAC.Using the modified mix design of the AAHFAC mix, it is found that the proposed mix design of the AAHFAC in this study meets the strength requirement.is mix design would lay a foundation for the future use of AAHFAC in construction industry.

Figure 1 :
Figure 1: Flow chart for the mix design procedure.

( 6 )
Step 6: calculation of individual mass of AAS content (NaOH and Na 2 SiO 3 solutions)

Figure 3 :
Figure 3: Test setup for compressive strength, modulus of elasticity, and Poisson's ratio.

Table 1 :
Chemical compositions of FA (by weight).

Table 2 :
Material properties of the AAHFAC ingredients.

Table 3 :
[31]mum water content and percentage of air per cubic meter of concrete[31].

Table 4 :
Density of NaOH solution with different concentrations.

Table 5 :
Mix proportion used in this study based on the mix design procedure.
, Poisson's ratio for

Table 5 and
, the 24 different mixes of the AAHFAC were conducted to develop the mix design methodology.e 28-day compressive strength of the AAHFAC cured at ambient temperature ranging from 15 to 35 MPa was obtained by using the proposed mix design methodology.All obtained compressive strengths of the AAHFAC mixes can be separated into 5 strength requirements, namely, 15, 20, 25, 30, and 35 MPa, respectively.